The researchers proposed here are designed to assess quantitatively the roles of membrane transport and of intracellular metabolism as rate determinants of the uptake of hexoses into animal cells. This is accomplished by comparing influx of series of substrates of increasing metablic complexity: a transported hexose which is metabolically inert, a hexose which is transported and phosphorylated, but not further metabolized, and fully metabolized hexoses like glucose and fructose. Flux analysis is carried out with a temporal resolution sufficient to follow the time-courses of attainment of steady-states, and thus to reveal the rate limitation imposed at each of the early steps of hexose utilization, and the apparent kinetic characteristics of a given step effective in situ. The cell systems to be examined from this perspective are normal hepatocytes vs. Novikoff hepatoma cells and chick embryo cells vs. their sarcoma virus-transformed counterparts. The comparison of results gathered with these cognate pairs will show which, or to what extent each, fo these determinants are altered by oncogenic transformation. The information should help define quantitatively the membrane or enzymatic steps which contribute to increased glycolysis in human cells - the "Warburg effect." It is, thus, information prerequisite to an efficient search for mechanisms of that effect, or the design of drugs which might exploit that effect.